1. A Field Of The Invention
The present invention relates to a new and improved system and method for cooling a medium, and more particularly, to a new and improved refrigerant power unit for cooling a medium such as ambient air or other fluid and to a new and improved method for using a refrigerant power unit to cool ambient air.
2. Description Of The Background Art
Mechanical refrigeration has been available for the last 150 years and has been used in a variety of circumstances that require a reduction or removal of heat from an enclosed area. The typical refrigeration cycle operates on the principle that a volatile refrigerant in liquid form will absorb heat upon evaporation. This change of state accomplishes the cooling effect in a refrigeration cycle.
Known refrigeration cycles include a compressor, a condenser, an expansion valve and an evaporator all in a closed loop. In this loop, the evaporator is the element in which cooling is performed and evaporation takes place. When liquid refrigerant flows from the higher pressure of the condenser to the lower pressure of the evaporator, its rate of flow must be controlled by a metering device. In the past, the metering device has been a thermal expansion valve. The refrigerant expands as it moves through the expansion valve. As this occurs, the refrigerant cools to the saturation temperature. To accomplish this cooling, the liquid must give up heat; and this heat is given to the nearest medium, which are adjacent molecules of refrigerant. Taking on this heat at the lower pressure vaporizes part of the refrigerant until the cool refrigerant vapor and the cool liquid refrigerant are in balance at the saturation temperature corresponding to the lower pressure. The vapor resulting from this vaporation is called "flash gas", and its amount is referred to as percent flash gas. Typical percentages of flash gas at air conditioning levels of temperature are usually in the range of 20 to 30 percent. This is an inherent part of a refrigerant cycle, and it detracts from the useful capacity of the cycle. It is therefore desirable that the refrigerant have a low specific heat so that the flash gas will be at a minimum.
For refrigerant to flow through the evaporator, there must be a pressure differential between the inlet and outlet of the evaporator. As the refrigerant flows through the evaporator, the pressure is lowered. The corresponding saturation pressure is also lowered; and the balance of liquid refrigerant must be cooled by further evaporation. The percent flash gas thus increases and the refrigeration effect decreases as refrigerant progresses into lower pressures in its path through the evaporator. As the refrigerant takes on heat from the medium being cooled, the balance of the liquid evaporates. In order to make full use of the refrigerant circulated, it is desirable to evaporate all of the refrigerant before it leaves the evaporator.
To maintain proper pressure, and hence, saturation or boiling temperature in the evaporator, it is necessary to pull off refrigerant vapor continuously and as rapidly as it is formed. This is the function of the compressor. If the compressor withdraws vapor faster than vapor is created by the load on the evaporator, the pressure, and hence, the temperature in the evaporator goes down. If the load increases and boils off refrigerant faster than the compressor withdraws it, the pressure and temperature rise.
To convert refrigerant vapor to a liquid so that it may be used again, the vapor must be condensed by removing heat from it. To do this, some medium to which the heat can flow must be used. To effect the desired heat flow, the temperature of the refrigerant must be higher than the temperature of the medium. A second function of the compressor therefore, is to raise the temperature of the refrigerant above the temperature of the medium. This is done by compressing the refrigerant which raises its temperature and permits the medium to cool the refrigerant and condense it to a liquid state.
Refrigerant leaves the evaporator and enters a compressor as either a saturated or super heated vapor. The refrigerant takes on heat during compression and leaves the compressor in a super heated state with more energy and hence more heat than it had when it entered the compressor. This increase in heat is referred to as the heat of compression and is equivalent to the work done on the vapor as it is being compressed.
Upon leaving the compressor, the refrigerant enters a condenser, also in the loop. In the condenser, heat is removed from the refrigerant by providing a medium at a lower temperature to which the heat can flow and be dissipated. The condenser removes heat taken on by the refrigerant in the evaporator and during the compression process. From the condenser, refrigerant is routed through the expansion valve back to the evaporator completing one cycle.
In many refrigeration systems of the type described, the different components are remotely located from each other, requiring long runs of refrigerant piping, electrical power and control wiring. This results in a loss of heat energy and the unit takes up a large amount of valuable space. It is desirable to provide a refrigeration system that minimizes flash gas losses and losses resulting from remotely located components, while requiring a small amount of space.